Apoptosis, or programmed cell death, is a naturally occurring process that has been strongly conserved during evolution to prevent uncontrolled cell proliferation. This form of cell suicide plays a crucial role in the development and maintenance of multicellular organisms by eliminating superfluous or unwanted cells. However, if this process goes awry, excessive apoptosis results in cell loss and degenerative disorders, while insufficient apoptosis contributes to the development of cancer, autoimmune disorders and viral infections (Thompson, Science, 1995, 267, 1456-1462).
Although several stimuli can induce apoptosis, little is known about the intermediate signaling events, including inhibition, that connect the apoptotic signal to a common cell death pathway conserved across many species. Recently, a family of apoptosis inhibitor proteins homologous to those produced by viruses has been identified in humans.
X-linked inhibitor of apoptosis or XIAP (also known as hILP and MIHA) is a member of the inhibitor of apoptosis (IAP) family of anti-apoptotic proteins which interfere with the transmission of intracellular death signals. It was first cloned as a regulator of apoptosis using a human X chromosome genomic sequence tagged site to generate primers to screen a human genomic library (Uren et al., Proc. Natl. Acad. Sci. USA, 1996, 93, 4974-4978). In these studies, X-linked inhibitor of apoptosis was identified as a factor that could inhibit apoptosis caused by the overexpression of interleukin 1 beta converting enzyme (ICE) or caspase-1, a protease required for apoptosis in mammals (Uren et al., Proc. Natl. Acad. Sci. USA, 1996, 93, 4974-4978). In addition the expression of X-linked inhibitor of apoptosis mRNA was shown to be highest in lung and brain (Uren et al., Proc. Natl. Acad. Sci. USA, 1996, 93, 4974-4978).
Subsequently, it has been shown that X-linked inhibitor of apoptosis inhibits other cell death proteases, specifically the processing of pro-caspases 3, 6 and 7 by blocking the activation of pro-caspase 9 (Deveraux et al., Embo J., 1998, 17, 2215-2223; Deveraux et al., Nature, 1997, 388, 300-304; Roy et al., Embo J., 1997, 16, 6914-6925).
Furthermore, X-linked inhibitor of apoptosis has been shown to play a role in signaling pathways that counteract the apoptotic signals generated by tumor necrosis factor alpha (TNF.alpha.) during inflammation (Stehlik et al., J. Exp. Med., 1998, 188, 211-216). X-linked inhibitor of apoptosis has also been shown to be regulated during follicular development of rat ovarian granulosa and theca cells suggesting a role for X-linked inhibitor of apoptosis in the control of stage-specific follicular atresia (Li et al., Endocrinology, 1998, 139, 1321-1328). Disclosed in PCT publication WO 98/22131 are methods of decreasing apoptosis in ovarian cells by administering a compound that increases the biological activity of an IAP polypeptide to modulate granulosa cell apoptosis which leads to follicular atresia (Tsang and Korneluk, 1998).
More recently, X-linked inhibitor of apoptosis was shown to participate in the bone morphogenic protein (BMP) signaling pathway as a positive regulator. In these studies, X-linked inhibitor of apoptosis was shown to interact with TAB1, an activator molecule for a MAPKK kinase known as TAK1 (Yamaguchi et al., Embo J., 1999, 18, 179-187).
Structural characterization of X-linked inhibitor of apoptosis showed that a single domain within the protein was responsible for its caspase-inhibitor properties (Takahashi et al., J. Biol. Chem., 1998, 273, 7787-7790). Disclosed in PCT publication WO 97/06255 are nucleic acid sequences encoding IAP proteins, polypeptides comprising the IAP proteins containing BIR domains and transgenic animals and cell lines that express the IAP family members (Korneluk et al., 1997).
Currently, there are no known compounds that effectively inhibit the synthesis of X-linked inhibitor of apoptosis. However, disclosed in PCT publications WO 97/40847 and WO 98/35693 are methods to inhibit the biological activity of IAP family members by administering to cells a compound that inhibits IAP polypeptides or the expression of the polypeptides for the treatment of neuronal and proliferative diseases, respectively (Korneluk et al., 1998; Korneluk et al., 1997). Antibodies, antisense oligonucleotides and other inhibitors of IAPs are also disclosed (Korneluk et al., 1998).
In light of the role X-linked inhibitor of apoptosis plays in inhibiting cell death pathways and their connection to the metastatic potential of cells, it is currently believed that agents capable of effectively inhibiting X-linked inhibitor of apoptosis function could serve as therapeutics for cancer and other hyperproliferative disorders.
To this end, antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in providing X-linked inhibitor of apoptosis inhibitors for a number of therapeutic, diagnostic, and research applications.